Generally NO. Here is the deal.
Both graphite and diamond are made of the
element CARBON, atomic number 6 on the Periodic
Chart. Now, the crystalline structure that
Carbon, and for that matter ANY element, takes
depends on the pressure and temperature.
These are called state variables, because
they determine the STATE of the element. So that
at very high temperature and low pressure,
carbon is a gas! At somewhat higher pressure
but still high temperature, carbon will become
a liquid Finally in another part of the
Pressure-Temperature space, carbon will take on a
crystalline form. The exact crystalline form or
POLYMORPH depends, again on the pressure and
So at 1 atm pressure (like in the room you are
reading this right now), GRAPHITE is the stable
form of carbon at T = 298 K (or 25 deg C or approx
70 deg F). Now at room temperature (298 K) if one
was to SQUEEZE the graphite in your pencil to
about 15,000 atmospheres, then in fact graphite is
no longer stable; instead a new crystalline form,
a mineral called DIAMOND is the stable phase or
state of the carbon.
So there is only a curve in PT space along
which BOTH graphite and diamond are stable. This
is called the equilibrium phase boundary
and it is an equation that relates P to T such
that ALONG THIS CURVE BOTH DIAMOND and graphite
coexist in stable equilibrium.
This subject is called chemical
thermodynamics and it is a powerful tool for
understanding the composition and energy exchange
in many, many biological, chemical, geological,
and physical systems.
No. Diamond and graphite have the same
chemical composition (carbon), but they form in
different situations. Graphite forms in a very
low pressure setting, and diamond forms in a very
high pressure setting (for example, buried
deep within the earth's crust).